It is common practice to employ partially reflective--partially transmissive metal layer-bearing films in glazing structures. These films may, be applied to the surface of glass window glazing materials. They may be laminated into glazing structures. They may be suspended alone or in combination with other sheets of glazing. These products are characterized by transmitting substantial proportions, such as at least 20% to as much as 90% or more of visible light while substantially reflecting heat and near infrared wave length radiation. These products typically have a plastic film substrate which carries the reflector metal layer adherent to it.
As will be described in more detail, plastic films are often marketed with a coating, known in the art as a slip coating, on one side to facilitate handling during production and fabrication. The side of the film having the slip coating is called (not unexpectedly) the "slip" side. The other side is the "nonslip" side. Slip coatings generally work by texturing the surface of the film. Two representative approaches to this involve surface texturizing by adding small particles to the plastic film as shown in U.S. Pat. No. 3,884,870 (American Hoechst) and applying and cracking an organic coating on the film as shown in U.S. Pat. No. 4,302,506 (also American Hoechst).
These reflector products, as a general class, may be prepared by applying the reflective layer to the film with a wide range of chemical mirroring methods, vapor deposition processes and sputter deposition techniques. In sputtering, a plasma is created between two electrodes in a high vacuum chamber. This plasma causes atoms of one electrode (the target), which is either metal or a metal compound, to be dislodged and drawn toward the other electrode. The plastic film substrate is placed between the electrodes and the material dislodged from the target is deposited upon the substrate.
Sputtering processes are often accompanied by a pretreatment step called preglow. Preglow also employs a plasma that is generated under conditions such that little or no material is deposited upon the substrate. As the name implies, "preglowing" commonly takes place immediately prior to the sputtering steps which involve actual material deposition on the substrate.
One simple format for these films used heretofore involves a single partially transparent metal reflector layer adherent to one side of the plastic film. Another widely employed format has a partially transparent, partially reflective sequence of dielectric and metal layers on one side of the film. Often these layers are in a dielectric-metal-dielectric sequence. In other cases more than one metal layer can be present with the several metal layers bounded by and optionally separated by dielectric layers.
Also in the past it has been proposed to place reflective layers on both sides of a plastic film. This has not found acceptance because the products do not have UV acceptable stability. This has been a vexing problem since double-sided materials do possess certain theoretical performance advantages. The most widely used plastic substrates are polyester materials, most commonly poly(ethyleneteryshthalate) or "PET". We observed that when double-sided polyester products, that is polyester-based materials having metal-layer-containing, heat-reflective structures on both sides, were prepared using art-taught coating methods the products degraded and yellowed prematurely.